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  1. #1
    Join Date
    Apr 2006
    Posts
    362

    Need advice regarding wire

    Posted this a few minutes ago in wrong forum. My apologies.

    Have my Geckos powered up, Mach3 installed, motors turning while connected to the drivers with their four 8" wires. Now I'm preparing to mount the motors which obviously will require more than 8" of wire. Someone said the wires had to be shielded. Can someone give me specific info regarding the exact type of wire I need to use, where to get it, where to get connectors so I can quickly disconnect the motors for maintenance. My motors are 640oz steppers. Also need to know the same things for the limit switches. Thanks

  2. #2
    Try this site:
    http://www.action-electronics.com/cabl-prc.htm

    They have connectors and multi conductor shielded wire

    Eric
    www.widgitmaster.com
    It's not what you take away, it's what you are left with that counts!

  3. #3
    Join Date
    Apr 2006
    Posts
    362

    Follow up question

    Thanks for the site. Do you know if I need shielded wire, and if so, why?

  4. #4
    Join Date
    May 2005
    Posts
    405
    Shielding stops electromagnetic interference. This can be interference from your router causing lost steps or your steppers interfering with the signals from encoders or limit switches. When you have problems due to shielding they can be quite hard to diagnose and rectify, so its far better to get it right first.
    Another thing that a lot of people don't realise is that shielded cables should have the shields all bonded to a common earth at one end only. Grounding both ends can result in earth loops and these can actually cause more problems than having no shielding at all.
    Paul

  5. #5
    Join Date
    Dec 2005
    Posts
    3319
    Over simplified response to post #3:

    Whenever you have current flowing in a wire, you create a magnetic field around it - simple earth science.

    The magnetic field can induce a current in an adjacent wire as the field builds and collapses. This is "noise" which is known as radio frequency interference as you build and collapse the field at faster and faster frequencies.....

    Stop this from happening, you use shielded wire (which must be connected to ground on ONE end only) as the current will tend to be generated/or prevented from being generated and conducted to ground by the shielding.

    This is an over simplification but it you ever tried to listen to a radio in a Corvette without shielded plug wires made of Pachard 440 copper wire, you'll know what the results of induced RFI is/are just by the sound (horrible static).

    "Noise" in the realm of CNC is the same as "out of control equipment"....

    If you drag a magnet across your computer screen, you can see visually what magnets do to precisely aimed electrons - namely create havoc

    When you lose control of electrons, you have all kinds of ugly problems.

    The explanation gets more complicated hereafter but that's the quick and dirty answer to why you need shielded cable....

  6. #6
    Join Date
    Apr 2006
    Posts
    362

    Follow up questions

    You have no idea how valuable answers 4 & 5 are to me. Because.... they not only answer my question(s), they also tell me WHY. But, sometimes good answers spawn more questions:

    1) Am I to assume that all four wires should be INDIVIDUALLY shielded? In my case there would be 3 motors x four wires or 12 wires for the 3 motors alone. Then the limit switches, etc. Don't get me wrong. If that's what it takes- that's what it takes. I just want to know is that's what you're saying. If so, where would I find wire like that?

    2) Am I to assume that the shield should be grounded at the end OPPOSITE the motor?

    3)How can grounding one end be different from grounding both ends? I really can't get my arms around that one. If one end of the cable is grounded isn't the whole cable, in effect, grounded?

  7. #7
    Join Date
    May 2005
    Posts
    405
    Re post 6
    1) Run one multi-cored screened cable to each motor. Use a cable that can handle the current draw of your motors here.
    Try and find some cheap multicored cable for your switches etc. Run all these together where you can to keep things tidy. There are cheap screened communications cables and some screened burgular alarm cables that are ideal for these and cost only cents per meter.
    Don't use single conductor type cables as they will eventually break.

    2) The common point that the cables run from is the controller box and its easiest to earth here.

    3) A signal induced into the shield can cause current flow if there is a complete curcuit to follow. When only one end is grounded there is no path, sort of like a battery and lamp. There can be no current flow until you connect both ends of the battery to the lamp.
    Crude anology but hope it helps.

    Paul

  8. #8
    Join Date
    Jan 2005
    Posts
    746
    If you connect the shield on both ends you can end up with what is called a ground loop. They can cause wierd things to happen (noise, humm...) and can be frustrating to track down when you have huge amounts of wires. I used to build large audio equipment rack systems, 10's of thousands of watts.
    If it's not nailed down, it's mine.
    If I can pry it loose, it's not nailed down.

  9. #9
    Join Date
    Apr 2006
    Posts
    362

    Screened?

    [QUOTE=paulC]Re post 6
    1) Run one multi-cored screened cable to each motor. Use a cable that can handle the current draw of your motors here.
    Try and find some cheap multicored cable for your switches etc. Run all these together where you can to keep things tidy. There are cheap screened communications cables and some screened burgular alarm cables that are ideal for these and cost only cents per meter.
    Don't use single conductor type cables as they will eventually break.

    Screened? Is this another word for shielded? Or are you talking about something else?

  10. #10
    Join Date
    Apr 2006
    Posts
    362
    [QUOTE=paulC]Re post 6
    1) Run one multi-cored screened cable to each motor. Use a cable that can handle the current draw of your motors here.

    I think you're saying that the four wires that operate the one motor are not shielded from each other, but there is a shield that wraps around the four of them as a bundle. Therefore, in a three motor system there are only 3 shields, not 12. So apparently I needn't worry about the yellow giving off bad vibes to the red and so forth. Right?

  11. #11
    Join Date
    May 2005
    Posts
    405
    [QUOTE=IQChallenged]
    Quote Originally Posted by paulC
    Re post 6
    1) Run one multi-cored screened cable to each motor. Use a cable that can handle the current draw of your motors here.

    I think you're saying that the four wires that operate the one motor are not shielded from each other, but there is a shield that wraps around the four of them as a bundle. Therefore, in a three motor system there are only 3 shields, not 12. So apparently I needn't worry about the yellow giving off bad vibes to the red and so forth. Right?
    Yep. You got it.

    Screened and shielded are the same thing. Sorry for swapping terminology.

  12. #12
    Join Date
    Dec 2003
    Posts
    24216
    Multi-Conductor Shielded cable can be obtained in Individually shielded, shielded pairs & overall shielded. There is also the cancellation effect of twisted pairs.
    For example, for every conductor feeding current to a device there is usually a return conductor, the radiated magnetic field of which, is in the opposite direction.
    So if this pair of conductors are twisted together, They tend to cancel the magnetic field set up around them, this coupled with shielding results in minimum EMR.
    Al.
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.

  13. #13
    Join Date
    Mar 2006
    Posts
    35
    Al

    I'm more of a visual person - so if you just for ie: you have two motors, the cables or wire running to both should be twisted together as far out to the motors as possible? Right?

    sorry - math word ??'s where my down fall

  14. #14
    Join Date
    Dec 2003
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    24216
    The conductors out to each individual motor can be twisted together, this does not mean collectively all motor conductors together which would be impractical.
    Al.
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.

  15. #15
    Join Date
    Apr 2006
    Posts
    362

    Illustrated

    [QUOTE=lemonyx]Al

    I'm more of a visual person - so if you just for ie: you have two motors, the cables or wire running to both should be twisted together as far out to the motors as possible? Right?

    From one visual person to another, let me suggest this illustration. Those in a position to know can tell us whether they accurately describe the choices.
    Attached Thumbnails Attached Thumbnails wire fixes.JPG  

  16. #16
    Join Date
    May 2005
    Posts
    405
    Your "best fix" would indead be the best but could prove to be expensive.
    Some cables have several twisted pairs with a shield around all conductors.
    This type of cable would be the ideal solution as there is little to be gained shielding the phases from each other. This type of cable is normaly used for communications purposes so you may have difficulty finding a cable of this type that has the current capability that you require. I think your diagram labled "ONE FIX" would be the most suitable for your hobby machine as you are more likely to find a suitable cable at an electronics store.
    Paul

  17. #17
    Join Date
    Nov 2005
    Posts
    938

    Jumping into the discussion feet first.

    I looked over the site Eric recomended and it doesn't appear that they have any reasonable heavy gauge wire. I was always told 22awg was to thin for the currents that a CNC needs to handle and most people have recomended 14 or even 12 to me (although 12 tends to get a bit stiff).

    Steven

  18. #18
    Join Date
    Apr 2006
    Posts
    362

    Oh crap!

    I just now realized something I should've considered before I began to focus on shielding: The wires coming from my motors are tiny! I don't know what gauge they are. I could guess. But instead, I'll put it this way: Using a drill gauge, I can put them through a 5/64" hole but not through a 1/16" hole (1.98mm go/1.59mm no go). That being the case-- will it do any good to have heavier wire for the cables? I guess it will. Not sure. Need to thnk about it. Need to hear from Paul and others.

  19. #19
    Join Date
    Dec 2005
    Posts
    1408
    [QUOTE=IQChallenged]
    Quote Originally Posted by lemonyx
    Al

    I'm more of a visual person -Those in a position to know can tell us whether they accurately describe the choices.
    Dear IQChallenged,

    You give yourself a too modest name.

    IMHO, the last cable arrangement is best.

    When wiring up a two phase stepper, I would run individual cables to each phase. Each cable should be a twisted pair with a braid screen. The braids should be earthed at the driver end, and not connected at the motor end. It is a "belt and braces" approach, and there will be some who will say it really isn't needed.

    Cable is cheap, problems are not.

    Best wishes

    Martin

  20. #20
    Join Date
    May 2005
    Posts
    405
    Quote Originally Posted by IQChallenged
    I just now realized something I should've considered before I began to focus on shielding: The wires coming from my motors are tiny! I don't know what gauge they are. I could guess. But instead, I'll put it this way: Using a drill gauge, I can put them through a 5/64" hole but not through a 1/16" hole (1.98mm go/1.59mm no go). That being the case-- will it do any good to have heavier wire for the cables? I guess it will. Not sure. Need to thnk about it. Need to hear from Paul and others.
    Bigger really is better. (Don't tell my wife)
    Thiner wire has more resistance so the thinner you go the more voltage loss to the motor.
    A thicker wire will also allow you to upgrade your motors at a later date without worrying.

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